#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int main(){
    char a;
    while(cin>>a){
        if((a>='a'&&a<='z')||(a>='A'&&a<='Z'))cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }
    return 0;
}
